docs(blocks): cross-link the Memory block from the Agent memory section

Final loss audit found the old page's pointer from built-in agent memory to the
standalone Memory block had been dropped; one line restores it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ouiliame

apps/docs/content/docs/en/blocks/agent.mdx

@@ -53,7 +53,7 @@ Built-in conversation memory, kept across runs by a conversation ID:
 - **Sliding window (messages).** The most recent N messages.
 - **Sliding window (tokens).** Recent messages up to a token budget.
 
-Memory needs a conversation ID to persist between runs.
+Memory needs a conversation ID to persist between runs. For memory that's shared across workflows or managed as its own store, use the [Memory](/integrations/memory) block instead.
 
 ### Response Format